Asphalt compositions are of great commercial importance since about 80% of the paved roads in the United States are composed of asphalt concrete and many of theses roads are urgently in need of repair as a result of increasing highway traffic. Furthermore, asphalt compositions provide the principle roof for thousands of homes throughout the country. Each must avoid stripping and rutting if their designated purpose is to be fulfilled.
The interaction of water and asphalt concrete may, under certain circumstances, cause stripping or loss of adhesion and consequential detachment of the asphalt from the aggregate. The result of such action decreases the cohesive strength of the mixture until it has no inherent structural strength as a paving material and approaches the condition of compacted gravel.
The need for reliable yet inexpensive means and methods to enhance the properties of asphalt concrete composition for road building and maintenance, roofing compositions and other applications, such as liners for waste disposal sites, has never been greater and is further magnified by the compelling need to maintain our nations infrastructure without increasing already outrageous governmental deficits.
In the prior art, sulfur, natural and reclaimed rubber and a variety of synthetic organic polymers have been mixed with the asphalt binder with a view to obtaining improved products. (See: U.S. Pat. Nos. 4,485,201 and 4,446,201) In an alternate, approach vinyl monomers and thermo-setting monomer combinations have been added directly to the asphalt and polymerized in-situ. (See: U.S. Pat. No. 4,333,866). The excessive cost and complex processing procedures required for these materials coupled with only marginal improvement obtained thereby, did not in general make any of these approaches attractive.
In another approach, highly reactive organosilane coupling agents as described in U.S. Pat. No. 4,038,096 and U.S. Pat. No. 4,036,661 were proposed for use in benzene solution to treat the aggregate and for direct addition to the asphalt binder. Such agents, which form organic-inorganic polymers, are reported to improve the anti-stripping properties of the asphalt concrete but are contraindicated because they are toxic and very expensive.
Slurry seal composites, prepared by precoating aggregate with a toluene solution of asphalt (cutback asphalt) containing a resin, were also proposed to improve adhesion but the evaporation of the toluene into the atmosphere creates severe air pollution problems. Treatment of sand with a mixture of an asphalt emulsion and an acrylic emulsion resulted in a composition which was proposed for use in patching or repairing asphalt concrete surfaces at ambient temperatures (U.S. Pat. No. 3,951,895).
Dilute aqueous solutions of water-soluble polymers, such as poly(vinyl alcohol), polyvinylpyrrolidone, and poly(ethylene oxide), are not effective for the use contemplated because the resulting films are sensitive to water and the modified asphalt aggregate compositions are no more resistant to stripping than are the asphalt compositions made from untreated aggregate.
Thus a clear need still exists for means and methods of producing new and improved asphalt concrete compositions which will substantially reduce, if not eliminate, stripping and rutting and the surface detachment and leaks in the asphalt surfaces produced therewith. It is toward the satisfaction of this need that the present invention is directed.